The next Evo Devo seminar will feature Dr Marketa Kauka, Group Leader at the Max Planck Institute for Evolutionary Biology, who will give a talk with the title"Genetic and developmental basis of mammalian face formation".
There is a remarkable variety of facial shapes in the animal kingdom that enables broad spectrum of functions and various skills. In addition to the obvious functional aspects such as protection of the central nervous system and the sensitive sensory organs, feeding as well as providing points for muscle attachment, the facial shape is important in many more ways. For example, humans use facial individuality for mutual recognition that assists social interaction, communication and affects numerous important aspects of everyday life. Pathological conditions include a wide spectrum of deficiencies, and may involve eating, breathing and speech impairments, and in some species, emotional problems and low quality of life in general.
The facial features reflect the underlying geometry of skeletal structures. Two types of stiff tissue, cartilage and bone represent the craniofacial internal skeleton. Bone is predominantly derived from pre-shaped cartilaginous templates that are formed during the embryonic development.
The first facial shapes are represented by forming mesenchymal condensations. The induction of mesenchymal condensation in specific location is instructed by signals coming from various sources, for instance from parts of the developing brain and olfactory epithelium. Enhancers influence the levels of these signals and this regulation may represent the genetic basis of facial individuality. Condensations turn into the cartilage that later expands tremendously while maintaining the perfect established 3D shape. The control of the shape and size during the whole embryonic growth of the mammalian face is based on uncoupled mechanisms of transverse integration of clonal columns of chondrocytes, control of the cartilage thickness, and existence of growth zones. Supplementary shape fine-tuning is later achieved by additional waves of mesenchymal condensations.
We found that basic 3D-blueprint of facial cartilages is induced as early mesenchymal condensations by combinatorial signals derived from epithelia and nervous system. We also revealed that the final shape and size of every solid cartilage structure in the embryonic head are achieved through two processes going in parallel: incremental addition of adjacently-induced chondrogenic condensations combined with scaling up of the pre-laid cartilage. The scaling is accomplished through previously unknown mechanism of growth based on introducing oriented clonal units into existing cartilage from perichondrial cell layer. We took advantage of various molecular tools to demonstrate how specific clonal dynamics in cartilage enables uncoupling lateral expansion from thickness control as well as geometrical fine-tuning. Interestingly, we found similar cellular mechanism operating in the developing finger digits and ribs (both regenerate quite remarkably in the framework of mammalian body) and during the growth and regeneration of salamander limb. Thus, it may represent evolutionary conserved mechanism of growth and shaping that allows substantial regeneration even in the adulthood.